Detection and quantification of analytes are of prime interest in medical, biochemical, analytical chemical, occupational safety, microelectronic, environmental, military, and forensic applications. Electrochemical sensors can be used for these applications. However, electrochemical sensors consume analytes, have long response times, are limited with regard to in vivo use, and are susceptible to poisoning by various contaminants. Optical sensing and probing are alternatives to electrochemical sensors. Various studies on optical methods of analyte detection have been reported in which a dye is immobilized in an analyte-permeable layer. In particular, these studies include sensors whose photoluminescence (“PL”) is affected by the analyte. Such affects may include a change in the PL intensity, spectrum, decay time, or polarization.
Commercially available optical sensors typically employ inorganic single crystal III-V compound light-emitting diodes (“LEDs”) as the light source. However, the need to incorporate optical components to convey light to the sensor and to collect the PL for readout increases complexity, size, and costs. Thus, single crystal III-V compound inorganic LEDs do not permit simple fabrication of integrated multisensor arrays.
In general, PL-based (bio)chemical sensors include a luminescent sensing element (the PL of which probes the analyte or agent), a light source that excites the PL of that element, a photodetector (PD), a power supply, and the electronics for signal processing. Light sources such as lasers or inorganic LEDs either may be difficult to integrate with the other components due to size, geometrical, or operational constraints, or they involve intricate integration procedures. In addition, they often generate heat, which can damage the sensing element or analyte.
Luminescent chemical and biological sensors detect changes in the PL intensity (IPL) or lifetime (τPL) of the sensing element caused by the analyte. In spite of potential widespread applications, the PD and light sources necessary to excite their PL typically have not been fully integrated with the sensing element. Consequently, the unintegrated devices are relatively bulky, costly, require trained operators, and are limited in their applications. As an example, the current commercial oxygen sensors for remote or local sensing, e.g., Ocean Optics FOXY sensor (see, e.g., www.oceanoptics.com), PreSense, and FCI Environmental Inc. employ GaN LEDs as the light source. The need to incorporate additional components such as optical fibers and their couplers to guide the light back and forth increases the size, cost, and complexity of the unit.
U.S. Pat. No. 6,331,438, the disclosure of which is incorporated by reference herein in its entirety, refers to an exemplary organic light-emitting device (“OLED”) excitation source and sensing element for analyte detection. What is needed is further integration of the PD and filters to provide very compact, robust, inexpensive, and autonomous sensors for real world applications, including multianalyte monitoring.